Cimetidine reduces impairment of cellular immunity after cardiac operations with cardiopulmonary bypass

Objective: Depressive effects of cardiopulmonary bypass on cell-mediated immune responses may lead to postoperative infectious complications. me previously reported that cimetidine reduced postbypass depression of the cytotoxic activity of natural killer cells, This study evaluated cimetidine as an agent to preserve cellular immunity after cardiac operations. Methods: In a prospective randomized study, 20 patients were divided into two groups of equal size. Cimetidine-group patients received 400 mg of cimetidine intravenously before bypass and a 33 mg/hr intravenous infusion of cimetidine after the operation, continuing until the fifth postoperative day, Control-group patients received conventional perioperative therapy, Lymphocyte subsets, natural killer cell activity, percentage of CD56(+)CD16(+) (percentage of natural killer cells), and percentage of CD11b(+)CD8(+) (percentage of suppressor T lymphocytes) were measured perioperatively. Results: Although temporary postoperative reductions in percentages of CD3(+), CD4(+), and CD56(+)CD16(+) cells were observed in both groups, CD8(+) percentages on postoperative day 1 and CD11b(+)CD8(+) percentages on postoperative days 1 and 3 in the cimetidine group mere significantly lower compared with those in the control group (p = 0.01, p = 0.004, and p = 0.02, respectively), Temporary postoperative reduction of natural killer cell activity was also observed in both groups, but the natural killer cell activity on postoperative day 1 in the cimetidine group (17.1%) was significantly higher (p = 0.02) than that in the control group (8.20%). Conclusions: Cimetidine counteracts depressive effects of cardiopulmonary by pass on cell-mediated immunity and may possibly reduce postoperative susceptibility to infection.